A “traditional backplane” is a circuit board (usually a printed circuit board (PCB)) having several electrical connectors that are connected in parallel with each other such that each pin of each electrical connector is linked to the same respective pin of all the other electrical connectors, thereby forming a computer bus. Such backplanes are typically used as a backbone to connect several PCBs together to form a complete computer/switch system. In such systems, the data is transmitted as electrical signals. As a result, when the data rate is high and the lengths of the conductors of the backplane over which the signals must be transmitted are great, signal integrity and power consumption become concerns.
Attempts have been made to overcome signal integrity and power consumption issues associated with traditional circuit board backplanes by using optical backplanes to interconnect electrical devices, such as integrated circuits (ICs) and PCBs. In optical backplanes, optical signals that have been converted from the electrical domain to the optical domain by electrical-to-optical (E/O) converters are coupled by a lens system of the optical backplane into an entrance facet of the optical backplane. The optical signals then propagate over optical waveguides of the optical backplane to an exit facet of the optical backplane. As the optical signals pass out of the exit facet of the optical backplane, they are coupled by a lens system of the optical backplane onto optical-to-electrical (O/E) converters, which convert the optical signals into electrical signals. The E/O converters are typically light emitting diodes (LEDs) or laser diodes. The O/E converters are typically photodiodes. The optical waveguides are typically optical fibers.
One of the disadvantages of optical backplanes of the type described above is that they require very precise alignment between the E/O and O/E converters and the respective lens systems and between the respective lens systems and the entrance and exit facets of the optical backplane. If the alignment between these elements is not extremely precise, optical coupling efficiency will be reduced and the corresponding optical signals will be degraded. This requirement for high-precision alignment imposes extremely tight tolerances on the manufacturing process, which increases the difficulty and costs associated with manufacturing the optical backplanes. In addition, the requirement for high-precision alignment becomes even more critical as the distance between the entrance and exit facets increases due to divergence of the light beam as it propagates through the backplane. Therefore, longer optical backplanes require higher precision alignment and therefore have tighter manufacturing tolerances. Consequently, longer optical backplanes are more difficult and costly to manufacture.
Accordingly, a need exists for an optical backplane that can be manufactured with more relaxed manufacturing tolerances and with longer lengths.